Abstract

Interactions involving hydrogen transfer were studied in a coculture of two hyperthermophilic microorganisms: Thermotoga maritima, an anaerobic heterotroph, and Methanococcus jannaschii, a hydrogenotrophic methanogen. Cell densities of T. maritima increased 10-fold when cocultured with M. jannaschii at 85 C, and the methanogen was able to grow in the absence of externally supplied H{sub 2} and CO{sub 2}. The coculture could not be established if the two organisms were physically separated by a dialysis membrane, suggesting the importance of spatial proximity. The significance of spatial proximity was also supported by cell cytometry, where the methanogen was only found in cell sorts at or above 4.5 {micro}m in samples of the coculture in exponential phase. An unstructured mathematical model was used to compare the influence of hydrogen transport and metabolic properties on mesophilic and hyperthermophilic cocultures. Calculations suggest the increases in methanogenesis rates with temperature result from greater interactions between the methanogenic and fermentative organisms, as evidenced by the sharp decline in H{sub 2} concentration in the proximity of a hyperthermophilic methanogen. The experimental and modeling results presented here illustrate the need to consider the interactions within hyperthermophilic consortia when choosing isolation strategies and evaluating biotransformations at elevated temperatures.

@article{osti_566365,
title = {Hydrogen transfer between methanogens and fermentative heterotrophs in hyperthermophilic cocultures},
author = {Muralidharan, V. and Hirsh, I.S. and Bouwer, E.J. and Rinker, K.D. and Kelly, R.M.},
abstractNote = {Interactions involving hydrogen transfer were studied in a coculture of two hyperthermophilic microorganisms: Thermotoga maritima, an anaerobic heterotroph, and Methanococcus jannaschii, a hydrogenotrophic methanogen. Cell densities of T. maritima increased 10-fold when cocultured with M. jannaschii at 85 C, and the methanogen was able to grow in the absence of externally supplied H{sub 2} and CO{sub 2}. The coculture could not be established if the two organisms were physically separated by a dialysis membrane, suggesting the importance of spatial proximity. The significance of spatial proximity was also supported by cell cytometry, where the methanogen was only found in cell sorts at or above 4.5 {micro}m in samples of the coculture in exponential phase. An unstructured mathematical model was used to compare the influence of hydrogen transport and metabolic properties on mesophilic and hyperthermophilic cocultures. Calculations suggest the increases in methanogenesis rates with temperature result from greater interactions between the methanogenic and fermentative organisms, as evidenced by the sharp decline in H{sub 2} concentration in the proximity of a hyperthermophilic methanogen. The experimental and modeling results presented here illustrate the need to consider the interactions within hyperthermophilic consortia when choosing isolation strategies and evaluating biotransformations at elevated temperatures.},
doi = {10.1002/(SICI)1097-0290(19971105)56:3<268::AID-BIT4>3.3.CO;2-V},
journal = {Biotechnology and Bioengineering},
number = 3,
volume = 56,
place = {United States},
year = 1997,
month =
}

Cells with and without hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity were used to examine the transfer of purine metabolites through the medium and via cell contacts. HGPRT{sup {minus}} Chinese hamster and human fibroblasts were able to incorporate {sup 3}H-labeled purine metabolite(s) from medium in which mouse HGPRT{sup +} B82 cells had been grown for 24 h with ({sup 3}H) hypoxanthine, but mouse A9 fibroblasts that were deficient in HGPRT, adenine phosphoribosyltransferase (APRT), and methylthioadenosine phosphorylase (MTAP) were unable to incorporate these metabolites. This suggests that in recipient cells incorporation is due to ({sup 3}H)MTA, which has been shown previously to be themore » major {sup 3}H-labeled purine metabolite to accumulate in B82 medium, being cleaved by MTAP to ({sup 3}H)adenine, which is phosphoribosylated by APRT to ({sup 3}H)AMP. Incorporation by recipient cells of metabolites from the medium is referred to as contact-independent metabolite transfer (CIMT). In autoradiograms of B82/A9 cocultures that were labeled with ({sup 3}H)hypoxanthine, grains were found over A9 that were not in contact with B82, although A9 did not act as recipients of CIMT. A9 were positive recipients of CDMT with only one of five cell lines tested, which suggested that these cells were selective communicators.« less

A process for the microbial desulfurization of natural gas based on the oxidation of H/sub 2/S(g) by Thiobacillus denitrificans has been previously proposed. The proposed process could be greatly simplified if aseptic operation of the reactor was not required. Accordingly, the authors report here a study of the effects of heterotrophic contaminants on H/sub 2/S(g) oxidation by T. denitrificans.

Anaerobic chemostats maintained at solids retention times of 15, 25, and 40 days were used to investigate the interaction between sulfate-reducing bacteria (SRB) and methane bacteria fed acetate and propionate. Organic loading rates of 0.25-0.50 g COD/L{center dot} d were used with feed COD/S ratios ranging from 60/1 to 2/1. Results indicated that SRB play an unexpected role in process failure. When systems failed, both sulfate reduction and methane production shut down. Levels of H{sub 2}S associated with irreversible failure were near 60 mg S/L for both acetate and propionate systems; corresponding total dissolved sulfide levels were 145 mg S/Lmore » for acetate systems and nearly 200 mg S/L for propionate systems. For similar loading conditions, propionate systems failed sooner than acetate systems. For the conditions tested, solids retention time had little impact on overall process performance and metal nutrition was not a problem. Estimates of the maximum tolerable sulfate loading rates are provided.« less